共查询到20条相似文献,搜索用时 15 毫秒
1.
Eva Daz Salvador Ordez Aurelio Vega Jos Coca 《Microporous and mesoporous materials》2004,70(1-3):109-118
The adsorption properties of a commercial Pd/Al2O3 catalyst were studied and compared with those of the Al2O3 support of the same specific surface area. Inverse gas chromatography (IGC) was used to determine the adsorption isotherms of five n-alkanes (C8–C12) in the 200–230 °C temperature range. Moreover, heats of adsorption, solubility coefficients and free energy of adsorption, are also reported. Interaction parameters of polar molecules with the stationary phase have also been determined and compared with those for the n-alkanes. Experiments with both the reduced and oxidized catalyst have been carried out by IGC and the results compared with those obtained by temperature programmed reduction (TPR) experiments. 相似文献
2.
Minglin Xiang Debao Li Haicheng Xiao Jianli Zhang Wenhuai Li Bing Zhong Yuhan Sun 《Catalysis Today》2008,131(1-4):489-495
Nickel and potassium promoted β-Mo2C catalysts were prepared for CO hydrogenation to higher alcohols synthesis. The results revealed that β-Mo2C produced mainly hydrocarbons, but the addition of potassium resulted in a remarkable selectivity shift from hydrocarbons to alcohols over β-Mo2C. Moreover, it was found that potassium enhanced the ability of chain propagation of β-Mo2C catalyst and led to a higher selectivity to C2+OH. The addition of nickel further enhanced higher alcohols synthesis, which showed the optimum at 1/8–1/6 of Ni/Mo molar ratios. The characterization suggested that there might be a synergistic effect of potassium and nickel on β-Mo2C, which favored the alcohols synthesis. The production of alcohols appeared to be relevant to the presence of Mo4+ species, whereas the formation of hydrocarbons was closely associated with Mo2+ and/or Mo0 species on the surface of β-Mo2C-based catalysts. 相似文献
3.
L. F. Liotta A. M. Venezia G. Deganello A. Longo A. Martorana Z. Schay L. Guczi 《Catalysis Today》2001,66(2-4):271-276
Selective oxidation of benzyl alcohol to benzaldehyde was carried out over pumice supported bimetallic and monometallic Pd and Ag catalysts. Preliminary kinetic studies were performed at 333 K in autoclave, at pressure of 2 atm in pure oxygen. Under these conditions, small amounts of benzoic acid were detected with the monometallic Pd pumice being the most active catalyst. The reaction was also carried out under flowing oxygen at atmospheric pressure and at 348 K. Under these conditions, the selectivity to benzaldehyde was 100%. The catalytic activity of the catalysts was measured after different oxidation and reduction treatments at high temperature. In addition, two mechanical mixtures of pretreated Pd and Ag monometallic samples were tested. The structural data (XRD, XPS, EXAFS) along with the catalytic results would indicate that Ag0 and Pd0 species are the catalytic sites acting with certain synergism. 相似文献
4.
Bijay K Sharma Mahendra P Sharma Sisir Kumar Roy Suresh Kumar Shilpa B Tendulkar Sanjeev S. Tambe Bhaskar D Kulkarni 《Fuel》1998,77(15):1763-1768
This paper reports the results of an experimental study involving Fischer–Tropsch synthesis on Co/SiO2–Al2O3 catalyst. The objective of the study was to find the reaction conditions for achieving an optimal selectivity with respect to
-liquid hydrocarbons. The experimental data on reaction conversion and steady-state concentrations of different product species has been used to develop artificial neural-network-based models which are generic and can be used for predicting the reaction behaviour under different operating conditions. 相似文献
5.
The role of H2O in the photocatalytic oxidation of toluene in vapour phase on anatase TiO2 catalyst: A FTIR study 总被引:2,自引:0,他引:2
G. Martra S. Coluccia L. Marchese V. Augugliaro V. Loddo L. Palmisano M. Schiavello 《Catalysis Today》1999,53(4):185-702
Photocatalytic oxidation of toluene has been carried out in a gas–solid regime by using polycrystalline anatase TiO2 in a fixed-bed continuous reactor. Air containing toluene and water vapours in various molar ratios was fed to the photoreactor irradiated by a medium pressure Hg lamp. Toluene was mainly photo-oxidised to benzaldehyde, and small amount of benzene, benzyl alcohol and traces of benzoic acid and phenol were also detected. In the presence of water, no decrease of photoreactivity was observed at steady-state conditions. By removing water vapour from the feed, the conversion of toluene to benzaldehyde was almost completely inhibited, and an irreversible deactivation of the catalyst occurred. FTIR investigations indicated that benzaldehyde is photoproduced on the TiO2 surface even in the absence of water vapour, but exposure of the catalyst to the UV light in a dry atmosphere results in an irreversible consumption of surface hydroxyl groups. As these species play a key role in the photoreactive process, this dehydroxylation should be the reason of the catalyst deactivation observed in the catalytic runs carried out in the absence of water vapour. 相似文献
6.
The recently discovered, high-temperature proton conductor, La0.99Sr0.01NbO4−δ, was used as a support for the electrochemical promotion of a platinum catalyst. Ethylene oxidation was used as a probe reaction in the temperature range 350–450 °C. Moderate non-Faradaic rate modification, attributable to a protonic promoting species, occurred under negative polarisation; some permanent promotion was also observed. In oxidative atmospheres, both the pO2 of the reaction mixture and the temperature influenced the type and magnitude of the observed rate modification. Rate-enhancement values of up to ρ = 1.4 and Faradaic-efficiency values approaching Λ = −100 were obtained. Promotion was observed under positive polarisation and relatively dry, oxygen-rich atmospheres suggesting that some oxygen ion conductivity may occur under these conditions. Impedance spectroscopy performed in atmospheres of 4 kPa O2/N2 and of 5 kPa H2/N2 under dry and slightly humidified (0.3 kPa H2O) conditions indicated that the electrical resistivity is heavily dominated by the grain-boundary response in the temperature range of the EPOC studies; much lower grain-boundary impedances in the wetter conditions are likely to be attributable to proton transport. 相似文献
7.
Heesoo Kim Ji Chul Jung Dong Ryul Park Howon Lee Joohyung Lee Sang Hee Lee Sung-Hyeon Baeck Kwan-Young Lee Jongheop Yi In Kyu Song 《Catalysis Today》2008,132(1-4):58-62
Nitrogen-containing mesostructured cellular foam carbon (N-MCF-C) was synthesized by a templating method using mesostructured cellular foam silica (MCF-S) and polypyrrole as a templating agent and a carbon precursor, respectively. The N-MCF-C was then modified to have a positive charge, and thus, to provide a site for the immobilization of [PMo10V2O40]5−. By taking advantage of the overall negative charge of [PMo10V2O40]5−, H5PMo10V2O40 (PMo10V2) catalyst was chemically immobilized on the N-MCF-C support as a charge-matching component. Characterization results showed that the PMo10V2 catalyst was finely dispersed on the N-MCF-C support via strong chemical interaction, and that the pore structure of N-MCF-C was still maintained even after the immobilization of PMo10V2. In the vapor-phase oxidation of benzyl alcohol, the PMo10V2/N-MCF-C catalyst showed a higher conversion and a higher oxidation activity (formation of benzaldehyde) than the unsupported PMo10V2 and PMo10V2/MCF-S catalysts. 相似文献
8.
The activity of a carbon supported PtWO3 (PtWO3/C) catalyst in the CO oxidation and CO2 reduction reactions was evaluated in sulfuric acid solution at room temperature.Cyclic voltammetry combined with on-line mass spectrometry shows that the oxidation of both saturated CO adlayer and dissolved CO on PtWO3/C material commences at rather low potentials, ca. 0.18 and 0.12 V vs. RHE, respectively. However, the low-potential process seems to involve only a minor fraction of the CO adlayer, the major part of the adsorbed CO layer being oxidised at the potentials as high as those for pure Pt catalysts—ca. 0.7 V vs. RHE. PtWO3/C material was found to reversibly de-activate upon a prolonged exposure to the CO-saturated solution due to the inhibition of the hydrogen tungsten bronze formation.The reduction of CO2 on PtWO3/C leads to the formation of an adsorbate - presumably CO - on the Pt sites of the catalyst. Although the rate of the adsorbate build-up on PtWO3/C at 0.1 V is lower than that on pure Pt/C, our results indicate that upon a prolonged exposure of the PtWO3/C electrode to a CO2-saturated solution a complete poisoning of the Pt sites with the adsorbate is likely to occur at room temperature. 相似文献
9.
Lu Gang Zhang Chengfang Cang Yanqing Zhu Zhibin Ni Yianhui Cheng Linjun Yu Fong 《Applied Catalysis A: General》1997,150(2):1-252
The performances of active carbon supported molybdenum sulfide catalysts prepared by different procedures or promoted by different elements in the synthesis of mixed alcohols from CO2 containing syngas were examined. The results showed that high alcohol activity and selectivity could be obtained by employing a rapid drying procedure and employing a H2S---H2 stream for (NH4)2MoS4 decomposition. Addition of Co, Cr and Cl to K---Mo/C catalyst led to an increase in the alcohol activity or selectivity. The presence of CO2 in the feed caused a greater amount of water to be produced but reduced the formation of CO2. The product distribution was also strongly influenced by the presence of either CO2 or H2S in the feed. Addition of CO2 reduces the formation of higher alcohols while H2S increases higher alcohol formation. 相似文献
10.
Nezahat Boz Nebahat Degirmenbasi Dilhan M. Kalyon 《Applied catalysis. B, Environmental》2009,89(3-4):590-596
KF-impregnated nanoparticles of γ-Al2O3 were calcinated and used as heterogeneous catalysts for the transesterification of vegetable oil with methanol for the synthesis of biodiesel (fatty acid methyl esters, FAME). The ratio of KF to nano-γ-Al2O3, calcination temperature, molar ratio of methanol/oil, transesterification reaction temperature and time, and the concentration of the catalyst were used as the parameters of the study. A methyl ester yield of 97.7 ± 2.14% was obtained under the catalyst preparation and transesterification conditions of KF loading of 15 wt%, calcination temperature of 773 K, 8 h of reaction time at 338 K, and using 3 wt% catalysts and molar ratio of methanol/oil of 15:1. This relatively high conversion of vegetable oil to biodiesel is considered to be associated with the achieved relatively high basicity of the catalyst surface (1.68 mmol/g) and the high surface to volume ratio of the nanoparticles of γ-Al2O3. 相似文献
11.
M. Kaneeda H. Iizuka T. Hiratsuka N. Shinotsuka M. Arai 《Applied catalysis. B, Environmental》2009,90(3-4):564-569
The present work has been undertaken to tailor Pt/Al2O3 catalysts active for NO oxidation even after severe heat treatments in air. For this purpose, the addition of Pd has been attempted, which is less active for this reaction but can effectively suppress thermal sintering of the active metal Pt. Various Pd-modified Pt/Al2O3 catalysts were prepared, subjected to heat treatments in air at 800 and 830 °C, and then applied for NO oxidation at 300 °C. The total NO oxidation activity was shown to be significantly enhanced by the addition of Pd, depending on the amount of Pd added. The Pd-modified catalysts are active even after the severe heat treatment at 830 °C for a long time of 60 h. The optimized Pd-modified Pt/Al2O3 catalyst can show a maximum activity limited by chemical equilibrium under the conditions used. The bulk structures of supported noble metal particles were examined by XRD and their surface properties by CO chemisorption and EDX-TEM. From these characterization results as well as the reaction ones, the size of individual metal particles, the chemical composition of their surfaces, and the overall TOF value were determined for discussing possible reasons for the improvement of the thermal stability and the enhanced catalytic activity of Pt/Al2O3 catalysts by the Pd addition. The Pd-modified Pt/Al2O3 catalysts should be a promising one for NO oxidation of practical interest. 相似文献
12.
Fabrication of Fe-, Ni- and FeNi-coated Al2O3 core-shell microspheres by heterogeneous precipitation 总被引:1,自引:0,他引:1
The precursors with NiCO3·2Ni(OH)2·2H2O-, Fe2O3·nH2O-, or both of NiCO3·2Ni(OH)2·2H2O- and Fe2O3·nH2O-coated alumina microspheres were prepared, respectively, by the aqueous heterogeneous precipitation using metal salts, ammonium hydro-carbonate and -Al2O3 micropowders as the starting materials. Subsequently, magnetic metallic Ni-, -Fe- and γ-FeNi-coated alumina core-shell structural microspheres were successfully obtained by thermal reduction of the as-prepared precursors at 700 °C for 2 h, respectively. Optimized precipitation processing parameters of the concentration of alumina micropowders (15 g/L), the rate of adding reactants (5 mL/min) and pH value were determined by a trial and error method. Powders of the precursors and the resultant metal (Ni, -Fe, γ-FeNi alloy)-coated alumina micropowders were characterized by scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS) and X-ray diffraction (XRD). The experimental results show that it is possible to adjust metal coating thicknesses and fabricate multilayer structured metal/ceramics core-shell microspherical powder materials and these materials may be applied for high performance of functional materials and devices. 相似文献
13.
研究了盐酸二甲胺三氧化铬/硅胶的制备方法及其对醇类的氧化性能。该试剂制备简单,制备与氧化过程中均不产生含铬废液,并且性能稳定、易保存。对醇的氧化反应收率高、条件温和、操作简单。为铬(Ⅵ)氧化剂用于清洁生产提供了依据。 相似文献
14.
The K2CO3/MoS2 catalyst for higher alcohols synthesis with synthesis gas as feedstock was prepared. The catalyst was characterized by TPR, in-situ XPS, XRD and SEM. Effects of pretreatment with H2, CO or synthesis gas on activity and selectivity of the catalyst were investigated. Results showed that there was a remarkable induction period about 180 h at the initial reaction stage for the un-treated catalyst. The catalytic performances for alcohols synthesis changed notably during the induction period. The induction period was confirmed to be resulted primarily from the sulfur losing and K element dispersion on the surface of ADM catalysts. Pretreatment of the catalyst could remarkably shorten the time of induction period as well as promote the catalytic activity. Furthermore, the higher alcohols (C2 + OH) content in the liquid products were enhanced after the catalyst pretreated by CO or synthesis gas which could be ascribed to the increasing of Mo4+ content on the surface of the catalyst. 相似文献
15.
16.
Antnio Emídio de Araújo dos Santos Jr. Dilce de Ftima Rossetti Haydn H. Murray 《Applied Clay Science》2007,37(3-4):281-294
Deuterium (δD) and oxygen (δ18O) isotope data from the Rio Capim kaolin, northern Brazil, were combined with optical studies in order to better understand the genesis and evolution of the kaolinites. The results show that δ18O values from a lower soft kaolin unit range from 6.0‰ to 19.2‰ for Ka (size ranging from 1 to 3 μm) and Kb (size ranging from 10 to 30 μm) kaolinites, and from 15.4‰ to 24.9‰ for Kc (size < 200 nm) kaolinites. The δD values range from − 63.1‰ to 79.5‰ for the Ka + Kb kaolinites, and from − 68.8‰ to − 244.35‰ for the Kc kaolinites. An upper semi flint kaolin unit, dominated by Kc kaolinites, displays δ18O and δD values ranging from 15.1‰ to 21.8‰, and − 71.3‰ to − 87.4‰, respectively. Based on these data, and on the δ18O and δD values obtained for the surface meteoric water and groundwater, it can be concluded that the kaolinites are not in equilibrium with the modern weathering environment, but they reflect isotopic compositions of the formation time, probably due to the interaction with fossil groundwater. However, mineralogical contaminations derived from replacements of framework grains also had great influence in the isotopic composition of these kaolinites. In addition, the isotope values of the Kc kaolinites from the semi-flint kaolin unit is variable, which is due to the presence of Kc kaolinites of different origins, including kaolinites derived from the underlying soft kaolin unit, kaolinites formed during different phases of paleoweathering, as well as later phases of coarse-grained kaolinites formed along fractures. Due to these complexities, binary diagrams contrasting δ18O and δD values, worldwide applied for distinguishing supergenic from hypogenic kaolinites, as well as those formed under weathering conditions, can not be applied to interpret the origin of the kaolinites in the Rio Capim Kaolin. 相似文献
17.
18.
Rafal Rachwalik Zbigniew Olejniczak Jian Jiao Jun Huang Michael Hunger Bogdan Sulikowski 《Journal of Catalysis》2007,252(2):161-170
Isomerization of α-pinene was performed on a series of dealuminated ferrierite (FER)-type zeolites in liquid phase at 363 K using a batch reactor. The course of zeolite dealumination was followed in detail using 29Si, 27Al, 1H MAS NMR, XRD, FTIR, and sorption of nitrogen. The ammonium form of FER was dealuminated with aqueous solutions of HCl. While retaining the crystallinity of the zeolite particles, the treatments removed up to 53% of the tetrahedrally coordinated aluminum atoms from the FER framework. According to 29Si MAS NMR studies, the framework aluminum atoms located at the 10-membered rings in the main channels of FER (TB sites) were depleted preferentially from their positions. Even relatively mild dealumination of FER led to an active catalyst containing both Brønsted and Lewis centers, yielding up to 97% conversion of α-pinene at 363 K, in contrast to the 72% observed for the parent hydrogen form. Such catalytic behavior was discussed in terms of the conversion of a reactant inside micropores of the zeolite catalyst, on Brønsted acid centers with enhanced strength located probably in the vicinity of Lewis sites. The selectivity toward camphene and limonene changed smoothly with the dealumination level; thus, a higher selectivity toward limonene was observed at the expense of camphene formation with increasing the nSi/nAl ratio of the catalysts. The selectivity toward camphene and limonene was close to 85% for all of the materials studied. The initial rates of α-pinene transformations over FER-type materials exceeded those observed for other catalytic systems, heteropoly acid/SiO2 and H2SO4/ZrO2. This study demonstrates the successful application of a medium-pore zeolite for the catalytic transformation of α-pinene in liquid phase. 相似文献
19.
La0.6Sr0.4Co0.2Fe0.8O3−δ powder was synthesized by a combined EDTA-citrate complexing process via low-temperature auto-combustion synthesis with NH4NO3 as an oxidizer and a combustion trigger. Two novel methods were explored to improve this auto-combustion technology with reduced NH4NO3 addition: the use of La0.6Sr0.4Co0.2Fe0.8O3−δ as the combustion catalyst and the application of asymmetric sol–gel process to provide the precursor with different NH4NO3 concentrations. The prepared perovskite powder was characterized by BET, SEM, XRD and iodometric titration techniques. The catalytic performance of the powder was also examined in the decomposition of peroxide hydrogen. Experimental results indicate that powders from catalytic combustion and asymmetric precursor routes have more advantages in terms of better crystallites, higher specific surface area, higher B-site valence state, improved sintering capability and better catalytic performance in peroxide hydrogen decomposition than that from the synthesis with uniform NH4NO3 distribution. 相似文献
20.
Valentina Ermini Elisabetta Finocchio Sara Sechi Guido Busca Stefano Rossini 《Applied Catalysis A: General》2000,190(1-2):157-167
The conversion of propane in the presence of oxygen over alumina has been studied using a fixed bed flow reactor. The interaction of the same catalyst with propane, propene, isopropanol and acetone has also been investigated, with additional gas-phase monitoring, in an FT-IR cell. Alumina looks active in the catalytic conversion of propane to propene, with the production of CO2, CO, ethylene, methane as the main by-products, depending on the reaction temperature. Higher hydrocarbons such as butenes, butadiene, benzene and toluene are also found.
This reactivity is mainly attributed to the weak but not negligible Brønsted acidity of the surface OH’s of alumina, possibly activating propane in the form of isopropoxides and allowing oligomerization of propene. This shows the detrimental effect of the uncovered alumina support in the case of alumina-supported catalysts for propane oxydehydrogenation and explains the positive role of doping with basic neutralizing agents such as potassium. 相似文献